Why do you need to see the levels in the tanks? Are you just doing a periodic inventory check or are you planning to control the tank level using the thermography? Since the tank walls are 1" thick and what you're looking at is only at 140 F, whatever you are able to see with the thermography won't be a very precise level.

I can also see this idea having issues as the ambient temperature gets closer to the product temperature, but is should work just dandy in cold weather.

Have you looked into the automated plumb-bob type level sensors? We use them here to check the levels in our grain bins and they work fairly well.

I need to know how much solids are deposited in a tank for cleaning, my manways are 30'' give or take from the floor, if i have a 6' hockypuck of solids (Cat, Minerals, trash) i need to know how much i need to remove or salvage and how do i get access into the tank, which if it is higher than the manway we have to go to a different rout to attack the problem.

We too use the psychical plumb-bob gage but they are not accurate, it only gives you a height where the plum-bob lands, crude oil and oil distillates dont settle its solids uniformly they have peak and troughs. Its not an option to install an electrical sensor on top of a crude oil tank even if its electrically safe. We have a $40,000 FLUKE IR but its 6 years old and technology has certainly passed us by with the readings we get and the quality of the report on the screen display.

I borrowed a FLIR One to inspect some central heating pipes buried in concrete below a tiled floor. The camera costs around £200 and adds on to an iOS or Android device. Is this the sort of thing you're after.